Malaria continues to be a global health problem where the mosquito Anopheles gambiae s.s. serves as a major vector for Plasmodium falciparum. Studying mosquito immunity is of grave importance because knowledge gained from these studies can be applied to future methods of abolishing the disease transmission cycle of malaria. One main aspect of mosquito immunity is the cellular response provided by hemocytes. Relevance of their importance comes from reports of TEP-1 and LRIM1, which are (1) produced solely in hemocytes and (2) are vital for malaria parasite clearance. This proposal will study molecular mechanisms behind regulating mosquito hemocyte homeostasis after a blood meal, and what affect this has on mosquito immunity to malaria parasites. The long-term goal is to understand the dynamics of cellular immunity in mosquitoes and its role in pathogen transmission. The specific aims are (1) determine a molecular mechanism of hemocyte proliferation after a blood meal, (2) determine a molecular mechanism through which hemocytes are cleared after blood meal-induced hemocyte proliferation, and (3) determine what role hemocyte homeostasis has on immunity. To determine what regulates hemocyte homeostasis, reverse genetics of pathways of interest and quantitative assays measuring hemocyte abundance will be employed. To determine what role hemocyte homeostasis has on immunity, Plasmodium berghei infection intensities will be determined in reverse genetic backgrounds of altered signaling in hemocytes after blood meal. Upon completion of these research goals, the molecular mechanisms responsible for regulating hemocyte numbers after a blood meal will be determined and their consequences on mosquito immunity elucidated. Importantly, this study will establish novel methodologies and paradigms for cellular immunity in insects that are likely to be applicable to other vector-borne diseases. The health relevance of this proposal is the importance of hemocytes in malaria parasite clearance, and the obvious benefits the mosquito has when the number of circulating hemocytes increases after blood meal.